This proposal intends to examine the mechanisms by which nontranslating messenger RNAs are recruited for translation. The system of choice to study such phenomena is the microinjected Xenopus oocyte. Using the injected oocyte I have shown previously that mRNAs which code for secretory proteins, but not for soluble cytoplasmic proteins, exist to a large extent in nontranslating ribonucleoprotein (RNP) particles. These stable, nontranslating RNPs are recruited onto polysomes when oocytes also are injected with heterologous rough endoplasmic reticulum (RER) or proteins salt washed from the RER. The methodology in the proposed research would include the injection of different mRNAs and putative regulatory molecules into the oocyte followed by the measurement of protein synthesis, cell fractionation, and the detection of mRNA by molecular hybridization and of protein by immunoprecipitation. These experiments would initiate in my laboratory long-term experiments intended to define protein-mRNA interactions and the control of gene expression at the translational level. Thus, an examination of the mechanisms involved in translational control is of critical importance in molecular, cellular, and developmental biology. The proposed research is directly related to health problems involving the secretion of proteins. For example, peptide hormones, antibodies, and digestive enzymes are secreted proteins; their potential inability to be secreted or their slow rate of secretion would be deleterious to the individual. Cystic fibrosis also is concerned with secreted proteins and the process of secretion. In more general terms, a knowledge of this "fine" central of gene expression is important for the understanding of the mechanisms underlying cell differentiation during development and also in the expression of cancers.